LONDON -- This was not the Serena Williams the tennis world is used to seeing on Centre Court. It was still good enough for the defending Wimbledon champion to advance to the second round in straight sets.
Struggling on serve and failing to dominate against a 148th-ranked Swiss qualifier playing in her first Grand Slam tournament, Williams labored to a 6-2, 6-4 victory Tuesday over Amra Sadikovic -- the 80th match win of her Wimbledon career.
What looked on paper like a complete mismatch turned into a tighter contest than expected.
"I never underestimate anyone," said Williams, who had only four aces and served five double faults. "It was a really good match, but I don't think it was tougher than I thought. It was definitely tough, but I always expect the best from everyone."
With her mother, Oracene Price, watching from the Royal Box, the six-time Wimbledon champion jumped out to a 3-0 lead, running off 13 points in a row at one stage, defying her reputation as a slow starter.
"I started fast -- that's about it," Williams said when asked what positives she took from her performance.
The 27-year-old Sadikovic, who decided to retire in 2014 to work at a tennis club in Basel but eventually was talked into returning to the tour, made things tricky for Williams. She took a 2-1 lead in the second set and stayed even until the final game, when she was broken while serving at 4-5.
The match ended on a successful line challenge by Williams after she hit a backhand return that was called long. After the video replay showed the ball hit the back of the line, Williams grinned and threw up her arms in triumph.
Williams, who finished with 19 winners but also had 18 unforced errors, was animated throughout the match as she tried to lift her game.
"I'm always shouting at myself and pushing myself, so it's absolutely nothing different," she said.
Since winning last year's title, Williams has come up short in the majors, losing in the semifinals at the U.S. Open and finals of the Australian and French Opens. She needs one more Grand Slam championship to equal Steffi Graf's Open-era record of 22 titles.
At her postmatch news conference, Williams was asked how much she thinks about equaling that record.
"I think more or less about winning Australia, I think about winning the French Open," Williams said. "Didn't happen. I think about winning Wimbledon. I don't necessarily think about winning 22.
"Mentally I've been further down than anyone can be. Well, maybe not anyone, but I've been pretty low. There's nothing that's not mentally too hard for me."
Williams said she isn't fatigued but is motivated to win Wimbledon once again.
"I would be lying if I said I feel fresh, but I don't feel fatigue," she said. "I don't think I feel fresh, but I feel real hungry, super motivated, extremely ready to do the best."
In a first-round contest played under the Centre Court roof, Svetlana Kuznetsova beat Caroline Wozniacki 7-5, 6-4 in a match between two former No. 1 players.
The 13th-seeded Russian, playing in her 13th Wimbledon, held off a late charge from the 45th-ranked Wozniacki, who was unseeded at a Grand Slam for the first time in eight years.
Kuznetsova has reached the Wimbledon quarterfinals three times -- in 2003, 2005 and 2007.
The retractable roof was closed for the match -- the third on Centre Court -- after the first rain delay of the tournament, which suspended all matches on the outside courts.
Other first-round winners included No. 6 Roberta Vinci, No. 19 Dominika Cibulkova , No. 27 Coco Vandeweghe and No. 30 Caroline Garcia.